1. Field of the Invention
The present invention concerns a multi-stage high-pressure compression installation formed of at least two compressors connected in series by means of at least one pipe.
2. Related Art
This type of high-pressure installation is used for example in the production of PET bottles, whereby the use of compressed gas with a pressure of more than 2000 kPa is required.
It is known, in order to use gas pressures of 2000 kPa or more, to mount two volumetric compressors in series and to provide a first gas tank at the output of the first compressor, whereby the output of the tank is connected to the inlet of the second compressor which is part of what is called the excess pressure compressor.
At the output of the aforesaid excess pressure compressor is in this case preferably provided a second tank which serves as a buffer for a user network.
In a known multi-stage compressor of this type, the drive of the first compressor is controlled as a function of the pressure prevailing in the above-mentioned first tank, whereas the drive of the excess pressure compressor is controlled as a function of the pressure prevailing in the second tank.
The above-mentioned control implies that a compressor concerned runs under load and, consequently, only compresses gas when the pressure prevailing in the corresponding tank is lower than a preset pressure.
A disadvantage of a high-pressure compressor installation of the known type is that this installation reacts relatively slowly to major fluctuations in the compressed gas consumption.
Indeed, in case of a sudden increase in the compressed gas consumption, the pressure prevailing in the second tank will at first drop until a value is reached which is lower than the preset level for switching the excess pressure compressor into a loaded regime.
As soon as the excess pressure compressor is running under load, it will draw in compressed gases from the first tank, such that, subsequently, the gas pressure prevailing in this first tank will drop until it reaches a value below the preset level, such that the first compressor is loaded accordingly as well.
Due to the drop of the pressure prevailing in the first tank before the first compressor is turned on, the gas pressure prevailing at the output of the excess pressure compressor will not be constant at first, and this will be so until the first compressor runs at full load and consequently produces a quantity of compressed gas which is equal to the quantity of gas drawn in by the excess pressure compressor for the subsequent compression of said gas.
Another disadvantage of a known multi-stage compression installation is that the first tank between the two compressors must be relatively large in order to prevent all the gas in the first tank from being consumed, at the time the excess pressure compressor is being loaded, before the first compressor has been loaded.
It is clear that a large tank of this type, provided between the compressors, increases the space requirement of said compression installation which, as a consequence, will also be more expensive.